Advances in electronic devices generally include reducing the size of the components that form integrated circuits. With smaller circuit components, the value of each unit area of a semiconductor wafer becomes higher. This is because the ability to use all of the wafer area for integrated circuit components improves. To properly form an integrated circuit that employs a much higher percentage of usable wafer area, it is critical that contaminant particle counts on the semiconductor wafer surface be reduced below levels which were previously acceptable. For example, minute particles of oxides and metals of less than 0.2 microns are unacceptable for many of the popular advanced circuit designs, because they can short out two or more conducting lines. In order to clean a semiconductor wafer and remove unwanted particles, a process known as chemical mechanical polishing or chemical mechanical polish (hereinafter "CMP") has become popular.
CMP systems place a semiconductor wafer in contact with a conditioning pad that rotates relative to the semiconductor wafer. The semiconductor wafer may be stationary or it may also rotate on a carrier that holds the wafer. Between the semiconductor wafer and the conditioning pad, CMP systems often use a slurry. The slurry is a liquid having the ability to lubricate the moving interface between the semiconductor wafer and the conditioning pad while mildly abrading and polishing the semiconductor wafer surface. In this operation, it is important that there be a uniform layer of slurry at the interface between the semiconductor wafer and the conditioning pad. Too much slurry at the interface can cause too little conditioning or polishing by the conditioning pad. Too little slurry may cause too much conditioning. This is because the heat from friction that the semiconductor wafer experiences increases from a lack of lubrication, as well as the fact that more of the abrasive conditioning pad surface directly contacts the semiconductor wafer.
In conventional CMP systems, to ensure that a sufficient layer of slurry exists at the wafer-pad interface, the relative rotational speeds of the conditioning pad and semiconductor wafer are carefully controlled and somewhat limited. A greater speed for the conditioning pad relative to the semiconductor wafer, not only increases the removal rate of oxides, metals, and other contaminants on the semiconductor wafer, but also adversely affects the polishing uniformity. If it were possible to maintain more uniformity in the slurry layer at greater speeds, CMP process throughput could increase. This increased throughput could have numerous beneficial effects.